To sub or not to sub?

[Jonah]

Hi,

Another quick question if you please:

I'm a little confused as there seem to be conflicts of how laying flags should be done and I want to get it all straight in my mind before I go head first into my first hard landscaping project on my own to redo our patio and paving.

Sub base .... In the main site's article re laying flags it states: "This will not normally be required for a path or patio unless there is concern regarding the suitability of the sub-grade." There's only me and the missus so traffic will be very light. Some people in the forum say to do a job proper you need a sub base.

I want to skip the sub base if I can get away with it and put a sharp sand/cement mix down of 50mm on top of earth (not loose earth mind) and lay the flags on there. Will it be ok?

Thanks.

[surreyhillslandscapes.com]

50mm really isn't enough, the problem being that if the ground settles underneath your thin concrete slab will crack and the pointing in your slabs will too, and then your in all sorts of trouble. it's better to spend a little more time , effort and money now then have to re do it a year or so down the line.
I would put a minimum 150mm of type one base (limestone, crushed concrete), each whacked in 75mm layers.
If you decide to put down a sharp sand mix then at the very least make it 100mm, it should be fine but i wouldn't put my house on it. Make sure you have good drainage because from the photo it looks like it could be an issue..

[Rich H]

It's a bit of a vexed question really. The key thing is the subgrade. If it's heavily compacted gravelly soil or chalk, and you look out on a nice, even, flat lawn then the chances are you can just cut out the turf and lay the slabs straight on a bedding course on this compacted sub-grade. I'd agree that 50mm is a bit skinny, though.

On the other hand, if your soil is soft loam or clay, then a sub-base is required. You don't necessarily need much. I used to work with a very experienced and respected landscaper who never put down more than 50mm of type 1 for a sub-base. I prefer 75-100mm, even for a patio. Anything more than that would be overkill, unless you have fluid clay to contend with.

[surreyhillslandscapes.com]

"I used to work with a very experienced and respected landscaper who never put down more than 50mm of type 1 for a sub-base."

Wasn't tommy walsh was it Rich?

[Tony McC]

If your sub-grade is firm and stable with no organic matter, then you may omit the sub-base.

There's an FAQ here that helps further complicate the matter.

[lutonlagerlout]

what the gaffer says above is right,but as a pro i would always advocate at least 100 of MOT

if the local scallys hadnt nicked my cybershot i would take a picture of the existing patio at work
cheap slabs laid on 20 mm of building sand on mud

all over the shop,and the houseowner says to me "scuse tony would you mind ""straightening"" up the patio a bit?"

where to start?they have sunk ,risen, cracked ,the only straighting up it needs is into the skip.

if a jobs wort..... you know it by now

LLL

[Jonah]

Many thanks for your assistance so far.

Maybe it'd be more use to paint a fuller picture.

Looking at the photie below. The paved circle, I believe, was put in by the builders when the house was built (2000) and is stable, firm, and appears to be on a good base.

The rest of the cheapo Bean-Queue flags are laid using five blobs of mortar on earth (with some builders sand which was probably mixed in purely by chance).

What I intend on doing is lifting all the old flags, digging back the raised lawn (which is only raised by about six inches) for a new, square patio to be at the same level as the existing flags, as shown in the black line on the photie. I'm thinking of using some quality riven repro flags ... Bradstone "Old town" grey-greens in a random pattern. I'd appreciate any feedback on these particular flags?

I'm a software developer and systems engineer by trade, but I'm not shy of hard work and having a go at something I've never done before. Hence the paving project.

I'm trying to save a few quid by skipping the type-1 because in total I've got about 45m-square to re-pave and could do with cutting back on some materials if possible as we haven't got a big budget to play with.

BTW, the site really is an excellent source of information and I've read many of the articles over and over again to get my head around the whole concept and what's involved.

Thanks again.

[Jonah]

BTW, it's 45m square to cover as I want to replace the 12m square 3'x2' concrete flags which are down the side of the house and can't be seen in the photo.

[Jonah]

Blimey, I've just found that Midland Slate & Tile are only a couple of miles away from me.

I'll have to go over there tomorrow and see what they've got!

[lutonlagerlout]

jonah if you havent got a big enough budget save up untill you have
to quote john ruskin
"It's unwise to pay too much, but it's worse to pay too little. When you pay too much, you lose a little money — that is all. When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing it was bought to do. The common law of business balance prohibits paying a little and getting a lot — it can't be done. If you deal with the lowest bidder, it is well to add something for the risk you run, and if you do that you will have enough to pay for something better."
LLL :;):

[matt h]

a bit heavy for me at this time of night, but advise take your time, put in subbase and then sand over... it isnt that much more expensive really.

[James.Q]

...in order that a man may be happy, it is necessary that he should not only be capable of his work, but a good judge of his work.
either do or do not ;yoda; star wars :p

[matt h]

...in order that a man may be happy, it is necessary that he should not only be capable of his work, but a good judge of his work.
either do or do not ;yoda; star wars :p

And may the force be with you too!

[BGHSE]

I am preparing a garden patio using mix of 60x60, 60x30, 30x30cm 38mm thick slabs / flags.

Until I saw this thread I had intended to explain that I have Tony’s book and CD which seem to suggest a patio can be laid on 40/50mm screeded bed, but ground is clay, other than usual cracking in summer seems stable. Should I use sub-base?
Now I am more confused than ever. Tony says no, but useful if ground needs elevating – others say yes!
As I will need to excavate anyway I suppose the majority will advise me to put down Type 1. But how thick?
What is the majority verdict?


Marshall’s catalogue advises their more expensive slabs should be laid on full mortar, but that the cheaper slabs can be laid on screed.
Is their any logical reason for this advice?

The catalogue also advises that leaves should be swept from their Firedstone slabs to prevent staining, but makes no mention of the other ranges.
Does anybody know?

I have asked Marshalls, but they ignore me.


While looking at slabs for suitable selection, does anybody have any advice / experience of slabs from Castacrete in Strood (they told me of me this website), and Scott Bros. near Maidstone, and how they compare with Marshalls, Bradstone, Bretts, and the like?

I saw some moulds during a visit to Scott Bros. so they seem to manufacture on site, which could account for their prices being more competitive than others.


I am one of the dreaded DIY boys here so would very much appreciate all advice / guidance / experiences from the guys who know what they are doing.

[lutonlagerlout]

if you want it to last put in some kind of subbase ,be it hardcore or crushed concrete,you can lay directly on to subgrade but it wont last the course
a screeded bed is when you screed the whole area with semi dry mix at one time then lay the slabs on to that,this works with the cheaper ones as they tend to be flat faced and of an even thickness
the full mortar bed is when you are using wet cast decorative slabs or flags ,these tend to vary a bit in thickness and need to be laid with the top finish in mind ,so you lay them individually using a line or straight edge
hope this helps

1 tonne of mot should be enough for about 5-6 sq m @100mm so if you buy it at £25 a tonne its a good investment

LLL